6.085 Problem Set One
Hypothesis Testing

The CSV file contains data on cellphones per 100 people (source:
gapminder.org).  Complete the following analyses:

1. Do an exploratory analysis of cellphones in 1990 and 2007 by
   region.  Provide plots and describe major trends.  If we picked a
   European and an African at random, would the European be more
   likely to have a cellphone?

2. Did the number of cellphones in each country increase between 1990
   and 2007?  Describe the appropriate test and parameter settings.
   Show that the results match the corresponding one-sample test.
   What would happen if the two-sample test was run with incorrect
   settings for pooled standard deviation?  Incorrect matched pairs?

3. Is there a difference between the number of cellphones in Asia and
   Africa in 1990?  Explain the nature of the difference. How about in
   2007?

4. Is there a difference between the number of cellphones in North
   America and Europe in 1990?  How about in 2007?  How and why are
   the test results different than in Question 3?